A drugs test storm was threatening to overshadow the opening ceremony of the Olympic Games in Athens today with the future of Greek athletics hero Kostas Kenteris in doubt.

Kenteris, who had been expected to play a prominent role in tonight's ceremony, was instead facing a possible ban after missing a compulsory drugs test last night.

Then, in another twist, it was reported that the current Olympic 200 metres champion and Greece's favourite to win gold, had been involved in a road accident along with Olympic 200 metre silver medal holder Katerina Thanou.

The controversy erupted as final preparations were being made for the sporting spectacular in the city where it all began almost 3,000 years ago.

Kenteris had been expected to be handed the honour of lighting the Olympic flame for Greece in tonight's opening ceremony at the Olympic stadium.

The star was to be before the eyes of the world at the Athens showpiece, with an estimated four billion TV viewers tuning in and 77,000 spectators cheering him on in the stadium.

Instead his next big appointment is with an International Olympic Committee disciplinary investigation.

Former British gold medalist Lord Coe, chairman of the London 2012 Olympics bid, said missing a test was a serious matter.

He told BBC 5 Live: "He is Olympic champion. He is on every billboard in this city and he is the face of the games. Whatever the outcome, this is a very large story.

"A missed test is deemed to be a doping offence, followed by a two-year ban if the ban is upheld.

"We must be careful before making too many judgments but on the face of it the test was there and it wasn't taken."

If Kenteris and Thanou cannot come up with a plausible excuse for failing to take the test in the Athletes' Village yesterday, they will be expelled from the Games in disgrace.

After they failed to appear for the test Greek Olympic team spokesman George Gakis said: "They have been involved in an accident involving a motorcycle. They have been taken to hospital."

The accident happened near Glyfada, a southern Athens suburb where the Greek team has its training headquarters.

It has been reported that the injuries were "not just scratches".

Kenteris and Thanou arrived in Greece from Chicago yesterday and went to the Olympic Village, after which they were said to have been given leave to return to their homes to collect personal belongings.

The Hellenic Olympic Committee said in a statement before news of the crash came through that an IOC doping control representative came to the office of the Greek's team chief, John Papadogiannakis, to say he was looking for Kenteris and Thanou to get sample collections.

But he did not find the athletes in the Olympic Village.

The Greek team boss also searched for the athletes but they were not in their rooms.

The statement said a second official "explained the athletes left the village to collect some of their personal belongings from their home".

"He stressed the athletes were coming back and asked for a few hours' extension for them to return and submit themselves over to doping control."

Among the visitors to the Games is Tony Blair who arrived in Athens last night. The Prime Minister will lend his support to London's own hopes of hosting the event in 2012 during his stay with his wife Cherie. He is expected at the opening ceremony tonight.